Polychaete Nereis Virens Sars Research Articles

It's tough to be small: dependence of burrowing kinematics on body size

Burrowing marine infauna are morphologically diverse and range in size over several orders of magnitude. Whilst effects of ontogenetic and morphological differences on running, flying and swimming are relatively well understood, similar analyses of burrowing mechanics and kinematics are lacking. The polychaete Nereis virens Sars extends its burrow by fracture, using an eversible pharynx to exert force on the walls of the burrow. The resulting stress is amplified at the anterior tip of the burrow, which extends when the stress exceeds the fracture toughness of the material. Here we show that the polychaete Cirriformia moorei extends its burrow by a similar mechanism, but by using its hydrostatic skeleton rather than an eversible pharynx. Based on the dimensionless wedge number, which relates work of fracture to work to maintain body shape against the elasticity of sediment, we predicted that smaller worms would exhibit behaviors characteristic of tougher sediments and that scaling of kinematics would reflect decreasing difficulty in fracturing sediment with increasing body size. We found that smaller worms were relatively blunter and thicker, and had a greater variation of thickness than larger worms as they burrowed. Although these kinematic differences increase the stress amplification at the crack tip, smaller worms still generate lower stress intensity factors. The greater relative body thickness and shape changes of smaller worms are consistent with ontogenetic changes in forces exerted by earthworms, and are likely driven by the challenge of exerting enough stress to extend a crack with a small body size.

Oxygen and carbon dioxide exchange in the polychaete Nereis virens: influence of ventilation activity and starvation

The influence of ventilation activity and starvation on O2 uptake and CO2 production in the polychaete Nereis virens Sars was investigated during September 1986 using worms collected on intertidal flats outside the Naera Strand estuary, Denmark. The activity level, measured as ventilation rate, $$\dot V\prime _W $$ , was linearly related to active O2 uptake, $$\dot V\prime _{_{O_2 } } $$ , for worms inhabiting artificial burrows (i.e. tubes) in the laboratory. $$\dot V\prime _{_{O_2 } } $$ at 16°C was two and four times the extrapolated standard O2 uptake ( $$\dot V\prime _W $$ =0) when $$\dot V\prime _W $$ was 100 and 500 ml g-1 h-1, respectively. The use of tubes had no significant effect on N. viren's temporal ventilation pattern, Dv, compared to natural burrows in sediment. The ventilation rate, $$\dot V\prime _W $$ , however, was 2 to 3 times higher in tubes than in burrows. Starvation affected both ventilation and gas exchange. $$\dot V\prime _W $$ increased slightly during the first six days remaining constant thereafter. Dv, on the othe hand, decreased during the first six days followed by a gradual increase to Day 20. The observed decrease in Dv (%) from Day 0 to 1 was attributed to insufficient acclimation of the worms. The time integrated ventilation rate, $$\dot V\prime _W $$ × Dv, increased gradually throughout the 20 d starvation period. $$\dot V\prime _{_{O_2 } } $$ and $$\dot V\prime _{CO_2 } $$ declined rapidly during the first days of starvation. After 10 d the gas exchange reached steady levels at about 50% of the initial rate. The observed decrease in metabolic rate during starvation was explained by a rapid initial reduction in specific dynamic action (SDA) followed by a gradual exhaustion of readily available metabolic reserves, e.g. glycogen and lipids.

Effect of natural concentrations on nutrient exchange between a polychaete burrow in estuarine sediment and the overlying water

The exchange of inorganic nutrients; ammonium, nitrate and reactive phosphate between burrows of the infaunal polychaete Nereis virens Sars and the overlying water was assessed using V-shaped sediment cores. Exchange was determined by monitoring ventilation current and nutrient concentration of in- and excurrent water. Ammonium supply appeared independent of overlying water concentrations, showing a constant release of 0.5 μmol·h −1 (for a 2-g individual + burrow system) at concentrations from 2 to 87 μM. Of this release ≈40% originated from worm excretion, and the rest from microbial mineralization. Nitrate and phosphate exchange appeared very sensitive to overlying water concentrations, having equilibrium (zero flux) at 10–15 and 3 μM, respectively. Below these concentrations nitrate showed a slight release (due to nitrification), whereas phosphate was released at a rate of 3.2 × 10 −2 μmol· h −1 at 1 μM (mineralization and desorption). Above equilibrium they both were removed during water passage through worm burrows, reaching 0.4 μmol·h −1 for nitrate at 107 μM (nitrate reduction) and 3.7 × 10 −2 μmol· h −1 for phosphate at 5.6 μM (adsorption processes). The burrow system apparently acted as a buffer for phosphate and, to some degree, nitrate in the overlying water. At the study site (Norsminde Fjord estuary) nereid burrows were estimated to increase the sediment-water interface 150%. About 17% of the water column was cycled through the sediment by Nereis each day. The worm + burrow system was estimated to release 95 μmol· m −2·h −1 ammonium to the overlying water, which was ≈76–90% of the total release of ammonium from the sediment (30–36% was worm excretion).

Uptake of L-valine and other amino acids by the polychaete Nereis virens

For valine uptake by the polychaete Nereis virens Sars, the kinetic constants were: Vmax=355 nmol g-1 fresh weight h-1, Km=20 μM. Leucine and some other amino acids acted as partial inhibitors of valine uptake. Valine uptake rate was 78% higher at 21.5‰ S than at 14‰ S. The major portion of valine absorbed by the polychaete could be extracted as free valine, with 6.5 to 15.6% being respired, and 3.6 to 9.5% incorporated into proteins. Calculations indicate that 7 to 12% of the metabolism of N. virens may be sustained by uptake of glycine and aspartic acid from natural concentrations. It is suggested that uptake of amino acids by this worm is important in the nitrogen cycling of marine sediments.

The presence of alkenyl and alkyl glycerides, and choline and ethanolamine plasmalogens in a marine worm

1. 1. Crude lipid extracts of coelomic fluid, body wall and gut from the marine polychaete Nereis virens Sars were chromatographed on silica gel glass fibre sheets. 2. 2. Glyceryl ethers and neutral plasmalogens were found in unusually large amounts in coelomic fluid and body wall extracts but not in gut extracts. 3. 3. Phosphatidyl ethanolamine and phosphatidyl choline in all tissues gave a positive reaction to the plasmalogen test (method of Hack).

Cellulase in Nereis virens.

IN their communication about direct uptake of organic solutes, Chapman and Taylor1 commented on the contradictory published accounts of the food and feeding of the polychaete Nereis virens Sars. Verrill2 stated that it is carnivorous, while Gross3 suggested that it is almost entirely herbivorous. Turnbull4 regarded the animal as omnivorous. The principal recognizable remains that we found in the guts of N. virens collected at Southend, Essex, were shells of the small gastropod Hydrobia, small fragments of small cockle (Cardium edule) shells, and the alga Enteromorpha intestinalis. When kept in aquaria, N. virens readily ate the flesh of cockles, mussels (Mytilus edulis), and shore crabs (Carcinus maenas), when these were placed near the entrances to the burrows. The shell-valves of cockles, approximately 5 mm in diameter, were broken by the jaws of the worms and ingested. Large cockles and mussels were eaten only when they died and gaped open. Moribund cockles and mussels occur in large numbers at Southend, resulting both from natural mortality and the activities of the “bait-diggers”, who accidentally bury these molluscs in their search for Nereis. Enteromorpha was also readily ingested, but it was observed during these experiments that the faecal pellets of the worms frequently contained strands of apparently undigested algae. This posed the question whether Nereis can digest the cell walls of algae which it has eaten or whether it can only utilize contents of cells broken mechanically.